The goal of this Mentored Research Scientist Development Award (K01) is to prepare Dr. Dale Bond to become an independent scientist studying innovative behavioral approaches for the treatment of severe obesity, with specific emphasis on strategies to increase physical activity. Through a combination of didactic and direct mentored training experiences, this training plan will provide him with knowledge and skills in the following areas: severe obesity and bariatric surgical procedures; behavioral treatment of severe obesity, with emphasis on strategies to increase and measure physical activity; and methodology, statistics and the ethics of clinical trials in severe obesity. Dr. Bond will work closely with his mentor, Dr. Rena Wing, and his multidisciplinary team of co-mentors Drs. Harry Sax (surgeon), John Jakicic (exercise physiologist) and Joseph Fava (quantitative psychologist) throughout the course of the award. The resources at The Miriam Hospital/Brown Medical School combined with the mentoring by an expert advisory team will provide Dr. Bond with the ideal environment to achieve his long-term career objectives. The proportion of Americans who are severly [sic] obese or more than 100 pounds overweight is rapidly increasing. This presents a significant public health challenge as severely obese individuals have a higher rate of comorbidities and exact a greater toll on the health care system than less obese persons. For these individuals, bariatric surgery is currently the treatment of choice for producing substantial and long-term weight loss, although outcomes vary. Low physical activity is one behavioral factor that undermines surgical success. However, structured behavioral interventions to increase physical activity in bariatric surgery patients have not been conducted. Thus, the proposed study involves a randomized controlled trial comparing the effects of a behavioral intervention to increase physical activity, a behavioral intervention to decrease sedentary behaviors, and a standard care control group on changes in objectively-measured preoperative and postoperative physical activity among 75 adult bariatric surgery patients with low level of physical activity. The long-term goal of this research is to improve bariatric surgery outcomes through innovative behavioral strategies to increase physical activity.